1. Field of the Invention
The present invention relates to laser treatment processes and facilities and, in particular, to a method of manufacturing filters by laser treatment and a device therefor. More specifically, it is concerned with manufacture of filters, which are designed for extracting water from deep wells, by laser cutting of metals by the use of a flow directed towards a treatment point in conjunction with laser beams.
2. Description of the Related Art
Various filter designs running to about a hundred are currently in use, for example, gauze, wire, perforated edge and other filters. Accordingly, there are numerous production techniques.
In most cases, however, the known production methods do not provide for simple and reliable construction and their efficiency is fairly low, that is, the water intake surface of filters includes several layers, more specifically, a perforated tubular frame, steel guides, and a gauze or wire layer.
In other water intake filters, the construction is simplified by incorporating narrow slots, that is, by providing a single-component arrangement. However, with stamping and rolling techniques, narrow Y-shaped slots are obtainable only where sheet steel is utilized, a disadvantage substantially limiting the use of such filters in deep-water wells which amount to more than 90% of all artesian wells.
The known methods do not, at present, allow utilizing steel pipes for fabricating water intake filters with narrow Y-shaped slots, which would possess adequate hydrodynamic characteristics.
Also known in the art is a method of manufacturing filters by laser treatment and a device therefor, said device comprising an installation for laser treatment of tubes (of. JP, H, 60-223,692). The method includes such operations as laser cutting of tubes, heat treatment of their surfaces, and making of holes therein.
The known installation comprises mechanisms for attachment of tubes in a horizontal direction and for their displacement with a work table in the direction of the X coordinate; a mechanism designed to set a tube in rotation about its axis in two opposite directions; and an optical head directing a beam from a laser radiation source to a treatment point and focusing it to obtain a spot of a predetermined diameter in the area where laser treatment is to be carried out. Also, the installation incorporates means for moving the optical head both in a vertical direction and along the tube axis by means of a skew gearing arrangement.
An apparent disadvantage of the known method and the installation therefor is that the techniques involved do not permit obtaining taper slots since laser beam focusing resulting in a spot of predetermined diameter yields but a surface dimension of a hole without affecting a cross-sectional shape of a slot and quality of its walls. The power of laser radiation and the speed of movement of a tube being worked are dependent upon the capacity of the foregoing installation, the resultant limitations being associated with the need to satisfy stringent cutting requirements.
There is also known a device for manufacturing filters by laser treatment, which represents an automatic installation for gas-laser cutting of metals (SU, A, 958,060). The known installation comprises a continuous wave laser, a focusing lens, a nozzle for feeding working gas into a cutting area, and a work table with its drive mechanisms. The installation also includes a switching circuit and two pressure pickups, which are disposed under a cutting line. The first pickup is arranged at a distance equal to the radius of a focused laser beam from its axis in a direction opposite to the cutting direction, while the other pick-up is displaced relative to the first pickup in the same direction within a distance equal to the diameter of a jet of working gas coming out of a cutting cavity. The outputs of both pickups are connected through the switching circuit to the input of a mechanism controlling the work table drive speed and enabling manual and automatic control of a cutting speed. At optimum cutting speeds a part is completely cut through within a period of time at which a laser beam covers a distance equal to the diameter of a focused beam. The part being worked is cut through within a distance equal to the radius of the focused laser beam from its axis in a direction opposite to the cutting direction. The jet of working gas coming out of the cutting cavity passes between the pressure pickups getting into none of them. When cutting speeds are above or below an optimum value, the cutting is fully accomplished at a distance greater or, respectively, smaller than the radius of the focused laser beam. Consequently, the jet of working gas coming out of the cutting cavity deflects from its original position and gets into the first or second pressure pickup.
A major disadvantage of the foregoing automatic installation is that it does not include means for obtaining slots and cuts of desired shape. The use of pressure pickups as a means designed to check for optimum cutting conditions introduces unwanted complexities in the manufacture of filters by the use of the afore-mentioned installation, said limitation being associated with the need for cutting a plurality of slots and cuts around the periphery of a tube and throughout its length.
In a prior art method of manufacturing borehole filters by laser treatment (U.S. Pat. No. 4,317,023), fabrication of a filter with transverse slots involves focusing of a laser beam at a point lying somewhat higher than the outer surface of a plastic tube whereupon said tube is rotated about its longitudinal axis. A conical laser beam passing through the outer surface of the tube sublimates its material, thus forming an underlying internal slot whose walls diverge in the direction of the central axis of the tube.
The afore-mentioned method of manufacturing filters by laser cutting of dielectric materials is based on surface evaporation of a material without formation of a liquid phase. Due to the absence of heat conduction, all thermal energy is spent on evaporation of said material and, consequently, the profile of the formed slot follows the profile of the focused beam. The thickness of the material being cut is linearly dependent upon radiant thermal energy. Laser cutting of metals greatly differs from laser cutting of dielectric materials, as regards physical principles. When metals are to be cut, the presence of working gas, for example, oxygen or a suitable inert gas is necessary since the occurring process is characterized by exothermic reactions involving molten metal and working gas. In this case the cutting profile determines the heat-producing rate, which is dependent upon technological parameters of the working gas and laser beams whereby profiles may not be shaped as desired.